1. Field of the Invention
The present invention relates to a method for calculating a play time of a disc reproducing apparatus. More particularly, the present invention relates to a method for calculating a play time of a disc reproducing apparatus suitable for a time indication of a recording apparatus for a disc on which data has been recorded after compressed.
2. Description of the Prior Art
An optical disc system which records and reproduces digital audio signals to and from an optical disc or magnetooptical disc with a diameter of 64 mm (also called "Mini Disc") which is housed in a disc cartridge has been developed. On an optical disc which is used in the optical disc system, with sound compression technologies, the amount of original digital audio signals is compressed to around 1/5 times thereof and recorded. Thus, using a small disc with a diameter of 64 mm, digital audio signals can be recorded and reproduced thereto and therefrom for around 74 minutes long.
In a Mini Disc recording and reproducing apparatus, when data is recorded, laser power should be controlled. In addition, the interleave length of CIRC (cross-interleave Reed-Solomon code) is 108 frames, which is longer than one sector. Thus, a linking area is required. Therefore, on the optical disc, signals are recorded and reproduced cluster by cluster, each cluster consisting of 36 sectors. Data is recorded to 32 sectors of one cluster consisting of 36 sectors. The remaining four sectors are used for a linking area and a subdata area.
At the time of reproducing, data is reproduced from the Mini Disc at a higher transmission rate than that of a decoder which decodes compressed data. The reproduced data is temporarily stored in a buffer memory. The buffer memory becomes full with digital signals by around 0.9 seconds after they are stored therein. Even if digital signals stored on the disc cannot be read due to vibration or the like, the data stored in the buffer memory is output as reproduction signals for around 3 seconds. During this time, an optical pickup is accessed again to the original position and the signals are read. Thus, the Mini Disc recording/reproducing apparatus can prevent interruption due to so-called "track jump".
As a reproducing apparatus of digital audio signals, a compact disc (CD) reproducing apparatus has been widely used. When a disc is loaded on the compact disc reproducing apparatus, the total play time of the disc is displayed. In addition, while each music program is reproduced, the play time of the music program and the remaining play time are displayed.
Thus, for the recording and/or reproducing apparatus of the Mini Disc system mentioned above, there is the same desire as the compact disc reproducing apparatus. In other words, there is the desire that when a disc is loaded on the apparatus, the total play time of the disc is displayed and that while each music program is being reproduced, the play time thereof and the remaining play time are displayed.
On the conventional compact disc, a time code is recorded on Q channel of a subcode. On the innermost periphery of the disc, a TOC (Table Of Contents) is disposed. On the TOC, an absolute time at which each music program starts is recorded. Thus, when the TOC is read, the total play time of the disc can be obtained. In addition, with the information of Q channel of a subcode, the elapsed time of each music program can be obtained. Thus, the remaining play time of the disc can be obtained. Therefore, required time indication such as indication of the total play time of the disc, indication of the play time of each music program, and indication of the remaining play time of the disc can be relatively easily performed.
However, on the optical disc, the TOC does not contain the time information. In addition, as described above, the transmission rate of signals reproduced from the disc differs from that of data of the encoder which decodes compressed data. The signals reproduced from the disc are temporarily stored in a buffer memory. Thus, a signal at an address from which data is currently being reproduced does not accord with a sound which is currently reproduced. As a result, with an address at which the pickup is being currently accessed, the time information of a music program which is currently being reproduced cannot be obtained.